Our goal is to study the mechanisms of immune defense against tumors. Over the past year we have carried out the following projects: (1)\studies on the biochemical mechanisms of macrophage activation, (2)\purification and characterization of a cytotoxic factor from activated macrophages, (3)\studies on the mechanisms of chemoattractant action of lysophosphatidylcholine on lymphocytes, (4)\studies on the mechanisms of action of interleukin 1, and (5)\characterization of monoclonal antibodies against human leukemia-associated antigens.